Wear ring for a centrifugal pitot tube pump

ABSTRACT

In a centrifugal pump of the pitot tube type, a replaceable wear ring is positioned in the rotating assembly of the pump in that area of the rotating case which is most subject to erosion from the processing of abrasive fluids by the pitot tube pump. The replaceable wear ring can be easily and quickly replaced when eroded, thereby eliminating the need to replace the rotating case of the pump and eliminating the need for costly and time-consuming re-balancing of the pump.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a non-provisional application claiming priority toprovisional patent application Ser. No. 60/658,399 filed Mar. 3, 2005.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to centrifugal pumps of the pitot tube type, andrelates specifically to providing means for less expensively and moreconveniently repairing the rotating case of the pump when the rotatingcase is damaged as a result of processing abrasive fluids.

2. Description of Related Art

Pitot tube pumps are a type of centrifugal pump which generally comprisea pump casing that forms a housing for a rotating assembly thatsurrounds a stationary pitot tube. The rotating assembly furthercomprises a rotating case and a rotor cover that together serve toenclose the pitot tube. The rotating assembly spins at a very high rateand as fluid enters the spinning rotating assembly, it is directed tothe interior circumferential wall of the rotating case. The stationarypitot tube has an opening, or inlet, which is positioned in very closeproximity to the interior circumferential wall of the rotating case.Fluid moving at high velocity in the rotating case encounters the inletof the pitot tube and is pumped to the outside of the pump through thepitot tube.

Pitot tube pumps do not process fluids containing abrasive solids verywell. A pitot tube pump has a relatively high velocity of fluid rotatingin the pump at nearly the same velocity as the rotating case of thepump. As a result, some of the high velocity fluid enters the pitot tubeinlet and some passes by the stationary pitot tube. If the fluid beingprocessed contains abrasive solids, those solids will contact thesurface of the pitot tube and will erode it away. The abrasive solidsalso have a tendency to deflect off the area of the pitot tube near theinlet and cause erosion of the interior wall of the rotating case inclose proximity to the pitot tube inlet.

Many attempts have been made to improve the abrasive-resistant qualitiesof the pitot tube and rotating case. For example, pitot tubes have beenmanufactured with hard metal or ceramic inserts at the tube inlet, asdisclosed in U.S. Pat. No. 5,997,243. The pitot tube has also beenmanufactured with hard metal coatings and diamond coatings on thesurface. The rotating case has also been manufactured with severaldifferent material coatings, such as with hard metal coatings, ceramiccoatings and urethane coatings. All of these changes and coatings haveworked to extend the life of the components, but ultimately they havefailed.

Early attempts to repair worn rotating cases have also failed. Repairingthe worn out area of the rotating case by such means as welding has notbeen successful. The heat from welding tends to relieve the internalcasting stresses in the component, and the sides of the rotating casemove inward, thus compromising the register fit between the rotatingcase and the rotor cover. This fit is critical to the operation of thepump, and without it the pump will vibrate beyond acceptable limits.

Attempts have also been made to coat the worn area of the rotating casewith an abrasion-resistant coating, but the same adverse effects resultbecause of the heat required in the coating process. Even machining agroove in the rotating case to fill it with urethane will relieve theinternal stresses in the part and compromise the register fit.

Coatings have been difficult to maintain on the rotating case because,in operation, the case expands and contracts. As the rotating assemblyaccelerates from zero revolutions per minute (RPM) to operating speed(as high as 6750 RPM) the outside diameter of the rotating case expandsa few thousands of an inch from the centrifugal force acting on it. Therotating case also expands and contracts in the axial direction as theinternal pressure in the rotating case chamber changes during operationof the pump. This constant expansion and contraction of these surfacesduring pump operation tends to over-stress the hard coatings and breaksthe mechanical bond between the coating and surface of the rotatingcase. The coating then begins to flake off of the interior wall of therotating case, often damaging the pitot tube in the process.

Thus, it would be advantageous in the art to provide a means foreffecting repair of the interior of a rotating assembly of a centrifugalpump which is relatively easy, less costly and which allows the repairto be done on-site, thereby limiting the time that the pump must betaken off-line for repair.

BRIEF SUMMARY OF THE INVENTION

In accordance with the present invention, the rotating assembly of apitot tube pump is structured to receive a replaceable wear ring that ispositioned in the rotating assembly where the component is most subjectto wear due to pumping of abrasive fluids. When the original wear ringbecomes worn or damaged, it is removed from the rotating assembly, suchas by simply grinding off a few tack welds that secure it to therotating assembly, and is then lifted out of a preformed groove cast inthe rotating assembly that is sized to receive the wear ring. A new wearring is then placed in the groove and is secured in place.

While the notion of a wear ring seems simple, certain obstacles had tobe addressed and overcome in providing the present invention, namely,how to insert a wear ring into a groove in the rotating assembly, makesure that is it fully seated in the bottom of the groove so it will notmove during operation of the pump, keep it from rotating relative to therotating assembly, retain it in the groove during operation, be able toremove it from the groove and then replace it with a new wear ringwithout affecting the balance of the rotating assembly.

The most difficult obstacle to overcome was how to replace the wear ringwithout affecting the balance of the rotating assembly of the pump. Therotating assembly (i.e., the rotating case and rotor cover) weighs about150 pounds and is dynamically balanced to 0.15 inch ounces at 1000 rpm.This is a very accurate balance and is very expensive to achieve. Thislevel of balance is required to maintain the vibration levels withinacceptable limits for the life of the pump. In a pitot tube pump,balance and vibration are directly related. The better the rotatingassembly is balanced, the lower the vibration level will be whichresults in a longer bearing life for the pump. This level of balance isvery difficult to achieve by someone outside of the factory and is oftennever achieved in the field. Special tooling and structuring is requiredto achieve these levels.

Conventionally, to effect the rebalancing of a rotating assembly, thepump must first be removed from its place of operation and taken to arepair station. Removing the pump from its installation involvesdisconnecting the piping, seal flush lines and couplings, and unboltingthe pump from its base plate. Removal of the pump in this mannerrequires the pump to be re-aligned to the drive train when it isre-installed. Removal and re-installation of the pump can take fromseveral hours to several days depending on the complexity of the pumpoperating system. The pump then has to be completely disassembled and anew rotating assembly installed on the shaft. The rotating assembly hasto then be re-balanced. Then the pump can be rebuilt and re-installed onits base plate and re-aligned to the drive train.

The present invention avoids the conventional need for removing the pumpfrom its base, thereby compromising the balance of the pump. With thepresent invention, the front or suction side of the pump casing can beopened while it remains on its base plate, and the wear ring can bereplaced with relatively simple ease. Consequently, with the presentinvention, only the suction and discharge piping and the front of thepump need to be disassembled and then reassembled. The ease andsimplicity of replacing the worn wear ring results in significant laborsavings and reduces the amount of down-time of the pump.

Erosion in the rotating assembly (e.g., rotating case) happens in anuneven way, which causes the rotating assembly to become unbalanced.From the first instant that the pump is put into operation the balanceof the rotating assembly is being degraded. The ability to simplyreplace a wear ring and keep the pump within the balance specificationfor a longer period of its life results in longer pump operation withlower maintenance costs. These and other advantages of the presentinvention will become more apparent with the following detaileddescription of the invention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the drawings, which currently illustrate the best mode for carryingout the invention:

FIG. 1 is an isometric view, in cross section, of a prior artcentrifugal pump of the pitot tube type;

FIG. 2 is an isometric view, in partial cross section, of the rotatingassembly of the prior pump shown in FIG. 1, with the pitot tube assemblyremoved;

FIG. 3 is an isometric view, in partial breakaway, of a rotatingassembly of a pitot tube pump with the pitot tube assembly in positionwithin the rotating assembly;

FIG. 4 is a partial cross section view in elevation of the rotating caseand rotor cover, with the pitot tube assembly removed;

FIG. 5 is a partial cross section view in elevation of a rotor formed inaccordance with the present invention;

FIG. 6 is a perspective view of a wear ring of the present invention;

FIG. 7 is an isometric view, in partial cut-away, of a rotating assemblyof a pitot tube pump configured in accordance with the present inventionand illustrating the wear ring in position within the rotating assembly;and

FIG. 8 is an enlarged view of the rotating assembly configured inaccordance with the present invention and illustrating the securement ofthe wear ring in position within the rotating assembly.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a conventional centrifugal pump 10 of the pitot tubetype. The pump 10 generally comprises a pump casing 12 that forms ahousing for a rotating assembly 14 and a pitot tube 16. The rotatingassembly 14 further comprises a rotating case 18 and a rotor cover 20,the combination of which provide an interior space 22 within which thepitot tube 16 is positioned. The rotating assembly 14 is rotated by adrive shaft 24 connected to a motor (not shown). While the rotatingassembly 14 of the pump 10 rotates during operation of the pump, thepitot tube 16 is stationary.

FIG. 2 further illustrates just the rotating assembly 14 and drive shaft24 of a centrifugal pump of the pitot tube type, with the pitot tuberemoved. It may be seen more clearly that the rotor cover 20 isremovably secured to the rotating case 18 by means of a plurality offasteners 25, such as bolts. Further, the rotor cover 20 is formed withan opening 26 through which the pitot tube (not shown) extends when thepump is fully assembled. It can also be seen in FIG. 2 that the rotatingcase 18 is somewhat bowl-shaped in that the rotating case 18 has anaxially-extending peripheral wall 28.

As best illustrated in FIGS. 1 and 3, the pitot tube 16 is formed withan inlet 30 through which high velocity fluid enters as the rotatingassembly 14 rotates. The inlet 30 of the pitot tube 16 is positioned inclose proximity to the peripheral wall 28 of the rotating case 18 forthis purpose. When the high velocity fluid strikes the inlet 30 of thepitot tube 16, some of the fluid will enter the inlet 30, but some ofthe fluid is deflected by the pitot tube 16 and is thrown against theperipheral wall 28 of the rotating case 18.

When the fluid being processed by the pump contains solids, therebyrendering the fluid abrasive, the fluid that is deflected by the inlet30 of the pitot tube 16 eventually causes an area of erosion in theperipheral wall 28 of the rotating case 18, as depicted by the trough 34illustrated in FIG. 4. The trough 34 or area of erosion of the rotatingcase 18 is principally confined to that area of the peripheral wall 28that is directly adjacent the inlet 30 of the pitot tube 16. As notedpreviously, various attempts have been made to improve theabrasion-resistant character of the rotating case 18 in the area oftypical erosion, but without success.

FIGS. 5-8 illustrate the solution provided by the present invention. InFIG. 5, it can be seen that a groove 40 is formed in the peripheral wall28 of the rotating case 18 in that portion of the peripheral wall 28adjacent the position of the pitot tube inlet and, consequently, thatportion of the wall 28 that would be conventionally eroded by fluiddeflected away from the inlet of the pitot tube. The groove 40 is formedin the circumference of the peripheral wall 28 during the castingprocess and is sized is axial width and radial depth to accommodate aremovable wear ring 42, as shown in FIG. 6. Notably, while the groove 40is shown formed in the rotating case 18, it may be suitable to form thegroove 40 in the wall of the rotor cover 20 if the rotating assembly 14is so configured.

The wear ring 42 of the present invention is generally formed as a bandsized in axial width 44, length 46 and radial depth 48 to fit snuglywithin the groove 40 formed in the rotating case 18, as shown in FIG. 7.While the wear ring 42 is illustrated here as comprising a flattenedband, the profile in cross section, as taken through the radial depth 48of the wear ring 42, may be other than flat (e.g., triangular shaped) toconform to a selected similar shape of groove 40 formed in the rotatingcase 18. The radial depth 48 of the wear ring 42 is preferably equal tothe radial depth of the groove 40; however, the radial depth 48 of thewear ring 42 may be slightly greater or slightly less than the radialdepth of the groove 40. It is only important that the radial depth 48 ofthe wear ring 42 be sized such that the pitot tube does not impact thewear ring 42 at any time during operation of the pump.

The wear ring 42, which is most suitably formed of a hard metal, ceramicor alloy material, is formed in a manner that allows the circumferenceof the wear ring 42 to be slightly flexible or able to expand andcontract in an amount sufficient to allow positioning of the wear ring42 within the groove 40, and to allow removal of the wear ring 42 fromthe groove when replacement is required. As shown in FIG. 6, thecontractibility and expandability of the wear ring 42 may be provided byforming the wear ring 42 with two free ends 50, 52 that enable one end50, 52 of the wear ring 42 to be positioned in overlapping juxtapositionto the other end 50, 52 so that the circumference of the wear ring 42can be contracted an amount sufficient to fit the wear ring 42 into thegroove 40 formed in the rotating case 18.

Once positioned in the groove, as shown in FIGS. 7 and 8, the wear ring42 may then expand, or spring back, to its original position with thetwo free ends 50, 52 positioned adjacent each other as shown in FIGS. 6and 8. The wear ring 42 may be structured or configured in othersuitable ways to enable the wear ring 42 to be positioned in the groove40 of the rotating case 18, including a configuration where the wearring 42 is continuous (i.e., without free ends). As shown in FIG. 8,once the wear ring 42 is positioned in the groove 40, the two free ends50, 52 may be secured in position by any appropriate means, such as tackwelds 54.

When the wear ring 42 becomes eroded or otherwise damaged, the worn wearring 42 may be conveniently and quickly removed from the groove 40 inthe rotating case 18 and replaced with a new wear ring 42. For example,to remove the damaged wear ring 42 from the rotating case 18, the groove40 may be structured with a small notch 56, as shown in FIG. 8. Toreplace the wear ring 42, the tack welds 54 are broken to release thefree ends 50, 52 of the wear ring 42. An object, such as the blade of ascrewdriver or pocket knife, is positioned in the notch 56 and one ofthe free ends 50 of the wear ring 42 is thereby lifted from the groove40. The raised free end 50 can then be used to pull the worn wear ring42 from the groove. A new wear ring 42 may then be positioned in thegroove 42, making sure to position the free ends 50, 52 near the notch56, and may be tack welded 54 into place.

It may be appreciated from FIG. 1, that effecting a replacement of theworn wear ring 42 involves simply removing the front or suction casing60 portion of the pump casing 12, removing the rotor cover 20 from therotating case 18 and removing the pitot tube 16 from the rotatingassembly 14. Removal of those components of the pump 10 does not affectthe balance of the pump, and does not require moving any other portionof the pump which would compromise its installation. Therefore, it canbe appreciated that the wear ring of the present invention provides asignificantly improved means for effecting repair of the rotatingassembly caused by erosion or other damage. The wear ring of the presentinvention may be adapted for use in other types of pumps and,consequently, reference herein to specific details of the invention areby way of example and not by way of limitation.

1. A replaceable wear ring for a centrifugal pitot tube pump, comprising a band of hard material sized for positioning in the rotating assembly of a centrifugal pitot tube pump in proximity to the pitot tube inlet of the centrifugal pump, said band being sufficiently circumferentially flexible to allow said band of said wear ring to be positioned in an interior circumferential wall of the rotating assembly.
 2. The replaceable wear ring of claim 1 wherein said band further comprises two free ends positioned in adjacent proximity to each other.
 3. A centrifugal pump of the pitot tube type, comprising: a rotating assembly comprising a rotating case and an attached rotor cover which together form an interior space, said rotating assembly having an interior circumferential wall; a pitot tube positioned within said interior space of said rotating assembly; a groove formed in said interior circumferential wall of said rotating assembly; and a removable wear ring sized to be positioned in said groove.
 4. The centrifugal pump of claim 3 wherein said removable wear ring is formed as a band having circumferential flexibility for enabling insertion and removal of said band from said groove.
 5. The centrifugal pump of claim 4 wherein said circumferential flexibility of said band is provided by said wear ring having two free ends.
 6. The centrifugal pump of claim 3 wherein said rotating assembly is further configured with a notch formed adjacent said groove for enabling removal of said wear ring from said groove.
 7. The centrifugal pump of claim 6 wherein said groove is formed in said rotating case of said rotating assembly.
 8. The centrifugal pump of claim 3 wherein said groove is formed in said rotating case of said rotating assembly.
 9. A method for repairing the damaged rotating assembly of a centrifugal pump, comprising: providing a rotating assembly in a centrifugal pump wherein said rotating assembly has an interior space defined in part by an interior circumferential wall, said interior circumferential wall having a circumferential groove formed in said wall and having a replaceable wear ring positioned in said groove; accessing said interior circumferential wall of said rotating assembly for removal of said replaceable wear ring from said groove; removing said wear ring from said groove formed in said interior circumferential wall of said rotating assembly; and placing in said groove of said rotating assembly a new wear ring.
 10. The method according to claim 9 wherein said rotating assembly is further configured with a notch formed adjacent said groove in said rotating assembly, and further wherein said wear ring is removed from said groove by inserting a prying device into said notch for removal of said wear ring. 